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REGEX undesired behavior

Posted on 2008-10-04
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Last Modified: 2012-01-23
I have a regex in a flex (sorry this is flex fast lexical analyzer not adobe flex)  scanner that I am writting that is according to the compiler making another regex I have unmatchable.

The first regex is
[a-zA-Z][a-zA-Z0-9_]*

according to the compiler this first regex will match
"]" and "[" and thus make my regex for them useless.  Why is it telling me this?

I found that if I make the first regex [a-zA-Z][a-z0-9_]* it no longer gives me this warning
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Question by:evanj23
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6 Comments
 
LVL 84

Expert Comment

by:ozo
ID: 22642355
I don't see how the first expression will match "]" and "["
If it had been [A-z] or [Z-A], and your character set was ASCII, then it would match "]" and "["
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LVL 51

Expert Comment

by:ahoffmann
ID: 22645515
how is your language environment (LANG, LC_Type, etc.) set?
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Accepted Solution

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evanj23 earned 0 total points
ID: 22645980
I found a way around this issue, I place the [ ] above the other regex so it has a higher precedence, but am still curious what was going on.   I also thought of [A-z] or [Z-A] but this was not the problem I triple checked my code.  

How do I check my language environment?
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Expert Comment

by:ahoffmann
ID: 22657503
> .. I place the [ ] above the other regex
could you please post the complete set of rules

> How do I check my language environment?
printenv
set
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LVL 29

Expert Comment

by:dgofman
ID: 37478729
This question has been classified as abandoned and is closed as part of the Cleanup Program. See the recommendation for more details.
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